Scientific Abstract

Proposal No. IBD-0215R
Principal Investigator:  Jeremy D. Sanderson, M.D.
Applicant Organization:  King's College London (United Kingdom)
Project Title:  The persistence of bacteria in lamina propria macrophages in Crohn's disease: role in pathogenesis
Period of Award:  November 1, 2007 – December 31, 2009

The aim of this proposal is to investigate the link between E. coli and Crohn’s disease (CD). Specifically, whilst much previous work has focused on pathogenicity determinants of E. coli isolated in patients with CD, our proposal investigates the hypothesis that there is a primary defect in phagocytic function in IBD. In particular, macrophages, which have been shown to be laden with clusters of E. coli, appear unable to complete the usual process of bacterial killing. Viable bacteria therefore persist and are likely to aggravate or perpetuate the inflammatory response seen in the gut wall in IBD.

Using biopsy and blood samples taken from those undergoing colonoscopy for CD or for colorectal cancer screening (controls), we propose to undertake laser capture microdissection (LCM) to isolate individual macrophages. We will then analyse cytokine profiles and markers of macrophage activation by RT-PCR on mRNA extracted from dissected macrophages comparing bacteria-laden with bacteria-free cells, inflamed and non-inflamed mucosa and compare Crohn’s disease and controls.

In addition, we propose to use blood derived macrophage/monocytes to study their response in vitro to challenge from IBD-derived E. coli, examining differences in phagocytosis and lysosome function, cytokine production and macrophage activation between the patients and control subjects.

Finally, we will determine whether the presence of the IBD susceptibility polymorphisms (including CARD 15 and the autophagy gene, ATG16L1) influence the interaction between macrophage and E. coli.

If our hypothesis is correct, we expect to demonstrate a defect in innate immunity (in this case, macrophage function) in individuals with CD, which leads to bacterial persistence. The results should offer new avenues for therapy, either targeted specifically at bacteria, at the macrophage defect or both.